This invention relates to an air conditioning system for automotive vehicles, for regulating temperature, humidity and so on within a vehicle compartment.
In a conventional air conditioning system for automotive vehicles in general, the refrigerating circuit is composed of a compressor 1, a condenser 81, an evaporator 80, a liquid tank 83 and so on, as shown in FIG. 1.
In recent years, a capacity-controlled type compressor has been spreading as the compressor 1. According to the capacity-controlled type compressor, the capacity of the compressor can be controlled linearly in proportion to a thermal load on the system, so that the compressor can sufficiently cope with the thermal load. Thus, it is possible to enhance the cooling feeling. Moreover, the compressor 1 is not so frequently turned on and off as a fixed capacity type compressor, and chance shocks due to turning-on and -off of the compressor, which conventionally occurred at cycling control, are not frequently applied to an engine, or if any, such shocks are small, so that the drivability can be improved. As an example of the compressor of this capacity-controlled type, a compressor of wobble-plate type is known, in which the angle of inclination .theta. of the wobble plate is varied to control the refrigerant suction pressure Ps of the compressor 1, thereby automatically adjusting the capacity of the compressor in response to the thermal load, etc.
Specifically, the compressor 1 is provided with a suction-pressure control device D as suction-pressure charging means including an electromagnetic actuator 68. The suction-pressure control device D is controlled by an external electrical control signal outputted from thermal-load detecting means S, thereby correcting the suction pressure of the compressor. In this connection, a fast-idle control device (F.I.C.D.) is known, which operates to raise the engine rotational speed by a predetermined value when the compressor is driven under such a condition that the engine is in an idling state. According to the fast-idle control device, however, the engine rotational speed is raised by a constant amount regardless of the capacity of the compressor.
In the conventional air conditioning system for automotive vehicles, the capacity of the compressor and the rotational speed of the engine are controlled in a manner described above. Accordingly, the engine rotational speed is raised uniformly, even if the compressor is set to a low capacity so that torque required for driving the compressor is lowered. That is, when the required driving torque for the compressor is low, the engine rotational speed becomes excessively high relative to the required driving torque, which is not preferable from the viewpoint of power saving. On the other hand, when the compressor is set to a high capacity, and the required driving torque for the compressor increases accordingly, the torque becomes insufficient because the engine rotational speed is raised uniformly. Thus, there is the possibility that the engine stalls.